The present invention relates to a protective member to be provided within a pressure vessel of an accumulator which is generally used in various hydraulic systems for storing or damping fluid pressure or for transporting fluid by pressure, the protective member being provided for preventing any damage of a separating member dividing the interior of a pressure vessel into two sections when the separating member is forced on the ragged surface of a supporting cylinder arranged on the shrinking side of separating member at the limit of shrinkage.
In the prior art, such a protective device is constituted by interposing valve plates between a separating member and each of the communicating holes formed in a supporting cylinder. By virtue of such a mechanism, the damage of separating member due to direct contact to communicating holes is prevented when the separating member shrinks.
However, it is impossible to form many communicating holes over the whole periphery of the supporting cylinder because of the structure. Thus, the flow of fluid through these communicating holes has a low efficiency. Moreover, the fabrication cost for providing with valve plates is high.
In some prior art accumulators, the supporting cylinder comprises porous material which is composed by sintering metal powder. In this construction, when the shrunk separating member contacts directly with the supporting cylinder, the metal powder gives a protective effect from damage of separating member. Although the effect of metal powder as protective member increases as a finer metal powder is employed, the resistance to fluid flow increases so that the further finer powder cannot be used.
In consideration of these results, some attempts are made to obtain an appropriate resistance to fluid flow by selecting the particle size of metal powder. However, the mutual binding of particles is various. For example, three particles may adhere one another to form a triangle. In this case, the formed void is minute. If five particles sinters to form a ring as a result of bridging, the formed void is coarse. Consequently, sizes of open pores for fluid which comprise these voids scatter largely. The corresponding parts of separating member are forced into coarser open pores and a damage of the member can arise.
Besides, any metal particles constituting sintered body may detach from the material and enter the liquid. These particles can destroy the whole hydraulic system. These are the fatal drawbacks of the equipment of this kind.